The publication EP 0 525 263 A1 discloses a vacuum infusion process for producing fiber-reinforced plastics parts. In the known process, a plurality of layers of a fibrous material are inserted into a mold. Below and above the layers of the fibrous material there are respectively distribution media separated from the layers of the fibrous material by further layers made of what are known as peel-off plies. At the underside of the mold, below the lower distribution medium, there is a sprue channel, and above the upper distribution medium there is an extraction channel. The airtight sealed mold is evacuated by way of the extraction channel, and a liquid plastics material is sucked through the sprue channel here. This material becomes distributed via the lower distribution medium over the entire area of the mold and completely penetrates the layers of the fibrous material. After the plastics material has hardened, the distribution media and the peel-off plies are removed from the fiber-reinforced plastic.
Document WO 2007/038930 A1 has disclosed another method for producing fiber-reinforced plastics parts. In the known method, a porous material is used as distribution medium and can enter into bonding with the plastics material infused. The distribution medium remains in the finished part after the plastic has hardened. In particular, it can form a surface of the part.
In particular in the case of very large rotor blades with a total length of, for example, 50 m or more, it is advisable for reasons of strength to use not only glass-fiber-reinforced plastics materials but also fibrous materials with even higher strength. This is particularly true of the main spar caps which extend in the longitudinal direction of the rotor blades and which form the central load-bearing structures of the rotor blade and absorb the bending moments that arise. Carbon fiber-reinforced main spar caps are often used for rotor blades of this type. The carbon fibrous materials are very expensive, and because their properties, in particular their flow resistance with respect to the liquid matrix materials, differ from those of glass fibrous materials, it is often advisable that carbon fiber-reinforced main spar caps are prefabricated. They can by way of example be produced in a separate mold in a first vacuum infusion process. Once the plastics material has hardened, the prefabricated main spar cap can be removed from said mold and inserted into the mold for producing the half shell of the wind turbine rotor blade. The other components of the half shell are then added in a second manufacturing step and are saturated with a liquid plastics material in a further vacuum infusion process and thus bonded to the prefabricated main spar cap.
The presence of the prefabricated main spar cap in the mold, that is, of a large body which cannot be saturated by the liquid plastics material, places particular requirements on the infusion procedure. Here again, complete saturation of the fibrous materials has to be ensured. Air inclusions have to be avoided, as also do large-volume aggregations of plastic.
In order to obtain a dependable manufacturing process in this situation, experience has shown that it is advisable to arrange, in the surroundings of the prefabricated main spar cap, large-surface-area distribution media which promote rapid and uniform distribution of the liquid plastics material. These structurally irrelevant distribution media are completely saturated by the plastics material and remain in the part once the plastics material has hardened. This considerably increases the total weight of the rotor blade, and higher loads arise, in particular in the region of the connection of the rotor blade to the hub.